1. Field of the Invention
This disclosure relates to an apparatus configured to generate a terahertz wave or an apparatus configured to detect a terahertz wave.
2. Description of the Related Art
A terahertz wave is an electromagnetic wave having a component falling within a given frequency range in a range from 0.03 THz to 30 THz. In such a frequency range, many types of characteristic absorption coming from structure or condition of various substances such as biological molecules as a principal example exist. By using the characteristics described above, an inspection technology configured to perform analysis and identification of substances in a non-destructive manner is developed. In addition, application to a tomography apparatus configured to visualize interiors of substances, in which an imaging technology, a high-speed communication technology, and transmissivity of the terahertz wave are effectively utilized, is expected.
Examples of a method of achieving generation and detection of the terahertz wave include a method of irradiating a light conductive element with a femtosecond laser. The light conductive element is obtained by forming a semiconductor film provided with an antenna electrode at a minute space on a substrate.
In order to improve efficiency of isolating the terahertz wave outgoing from the light conductive element, or efficiency of importing the terahertz wave into the terahertz wave incoming into the light conductive element, a semi-spherical lens having the same degree of refractive index as the substrate having the semiconductor film formed thereon is used. The semi-spherical lens is used with a flat surface portion thereof tightly in contact with a surface of the substrate having the antenna electrode formed thereon.
In order to improve efficiency of isolating and the efficiency of importing of the terahertz wave, alignment of an optical axis of the semi-spherical lens (an axis of rotational symmetry) and the antenna electrode of the light conductive element is important.
As a method performing the alignment, Japanese Patent No. 4762944 discloses a method of fixing the positions of the semi-spherical lens and the light conductive element by fitting the semi-spherical lens and components such as the light conductive element in a plurality of depressed portions formed on a holder configured to hold the semi-spherical lens and the light conductive element. In this case, accuracy of alignment is determined by the processing accuracy or the size of the depressed portions.
In order to confirm whether the alignment between the semi-spherical lens and the element is achieved with high degree of accuracy, detection of the terahertz wave by actually using an apparatus configured to generate or detect the terahertz wave and observation of an intensity or an amplitude of the detected terahertz wave are needed. When the alignment is insufficient, the alignment needs to be performed again. In the case of the configuration as Japanese Patent No. 4762944, the apparatus needs to be disassembled once and assembled again. Therefore, alignment cannot be performed while observing the intensity or the like of the terahertz wave. Therefore, the operation of the alignment may become complicated.